The invention relates to a pressing tool for producing composite fiber components having a first tool portion and a second tool portion which is movable relative thereto, wherein the two tool portions form, in the closed state of the pressing tool, a forming cavity for receiving a semi-finished fiber product which is intended to be formed and have a tool surface which delimits the cavity.
During the production of composite fiber components, the so-called “Resin Transfer Moulding” method (RTM method for short) is often used. In this instance, a “dry” semi-finished fiber product which is not yet impregnated is inserted into a pressing tool which usually comprises a lower tool and an upper tool which can be displaced relative thereto. Both tools form in the closed state at least one forming tool cavity between them. After the semi-finished fiber product has been inserted into the cavity, the tool is closed and the tool cavity is filled with a plastics mass or resin mass (hereinafter referred to as the matrix) which is connected to the inserted semi-finished fiber product and which hardens under the action of pressure and heat. After the hardening operation, the pressing tool is opened in order to remove the fiber-reinforced composite fiber component produced in this manner. A corresponding RTM tool is known, for example, from DE 199 22 799 A1.
In particular in regions of the semi-finished fiber product which are subjected to a high degree of deformation during the processing in the pressing tool, the resin flow is made more difficult as a result of the powerful deformation of the fiber material. Therefore, it can readily result in the production of poorly impregnated or non-impregnated locations (so-called dry locations) or pores in the subsequent component, which weaken the strength thereof at least locally. In accordance with the severity of those weak locations, under some circumstances the component may no longer be suitable for the application it is provided for.
Those weak locations are generally prevented by attempting to avoid high degrees of deformation, for example, as a result of tool edges with small, sharp edge radii. However, the configuration freedom for the component geometry is thereby restricted in such a manner that implementation is not possible in all cases. Alternatively, therefore, attempts are made to obtain a better resin flow in all regions of the component by way of extended injection times in order to avoid the defective locations mentioned. However, the processing time for each component is thereby increased substantially.
An object of the invention is therefore to provide a pressing tool which allows, in a simple and reliable manner, dry locations to be avoided during the production of composite fiber components and, at the same time, a processing and injection time which is as short as possible to be achieved.
This and other objects are achieved with a pressing tool for producing composite fiber components having a first tool portion and a second tool portion which is movable relative thereto. The two tool portions form, in the closed state of the pressing tool, a forming cavity for receiving a semi-finished fiber product which is intended to be formed, and have a tool surface which delimits the cavity. At least one of the tool surfaces comprises at least two adjacent and mutually inclined or angled surface portions which are connected to each other by a curved transition portion. Furthermore, the curved transition portion has at least one channel-like recess which faces the forming cavity.
The pressing tool described therefore includes at least the two tool portions (for example, an upper tool and lower tool) which, as a bottom die and upper die, have a three-dimensionally formed tool surface and engage one in the other when the pressing tool is closed in order to confer a corresponding, three-dimensional form on the semi-finished fiber product inserted therein.
In other words, therefore, the three-dimensionally formed tool surface delimits the cavity and consequently acts in a forming manner for the semi-finished fiber product which is intended to be formed. To this end, the tool surface usually has a plurality of surface portions which are inclined differently relative to each other or which are orientated in an angled manner relative to each other. Each of those surface portions may be constructed in a planar (substantially two-dimensional) or three-dimensionally formed manner, in particular curved.
There may be provided between adjacent and differently inclined surface portions a curved transition portion, via which the surface portions are connected to each other. The transition portion is itself also a portion of the tool surface and constitutes a “flowing” constant transition of the two surface portions relative to each other. Generally, the transition portion is curved more powerfully than the surface portions so that in the region of the transition portion the semi-finished fiber product is subjected to higher degrees of deformation at least locally than as a result of the surface portions themselves.
For example, great degrees of deformation, in particular degrees of deformation between 30° and 90°, which can negatively influence a resin flow, may occur in accordance with the angling of the surface portions relative to each other when the pressing tool is closed in the region of those transition portions.
The one or more recess(es) of the transition portion are provided in order to allow a matrix flow in the region of the curved transition portion in spite of the deformation of the semi-finished fiber product and consequently the reliable impregnation thereof. This is carried out in that the matrix is directed through the recesses outside the semi-finished fiber product into the regions of the more powerful deformations and, at that location, can be introduced into the surface of the semi-finished fiber product in an inward direction from the recess. Consequently, the formation of dry locations or pores is prevented in an effective and simple manner. An extension of the injection time is also unnecessary.
The one or more recess(es) is/are preferably constructed as so-called “perforations” and can readily be formed in the tool surface.
The curved transition portion may have, for example, a convex or concave curvature. In both cases, the matrix is introduced via the recesses into the regions of the curved transition portions in order to impregnate the correspondingly deformed locations of the semi-finished fiber product in a secure and reliable manner.
The at least one recess preferably extends from an end of the curved transition portion, which end adjoins the first surface portion, as far as an end of the curved transition portion, which end adjoins the second surface portion. This has the advantage that both ends of the recess are arranged in regions of the tool surface which do not have any curvature or have only slight curvature. Therefore, the matrix can be distributed in a practically unimpeded manner at that location so that dry locations do not occur in those regions. In addition, the matrix can be introduced into the recess via the ends of the recess which are provided in those regions and can flow in the extent direction of the recess. The matrix is reliably introduced via the recess into the (more powerfully) curved region of the transition portion and also ensures at that location the impregnation of the semi-finished fiber product.
In accordance with another embodiment, the at least one recess can extend from an end of the curved transition portion, which end adjoins the first surface portion, as far as a location in the second surface portion. In this instance, the end of the recess arranged in the second surface portion is preferably nearer a gate system for supplying the matrix than the opposite end of the recess, which end is associated with the first surface portion. For example, the recess may project from 2 to 50 mm, preferably approximately 10 mm, into the second surface portion. Naturally, the recess may also project, where applicable, into the first surface portion in the same manner and to the same extent.
For example, the curved transition portion may be constructed as a rounded edge. This means that the transition portion defines a portion in which the two surface portions meet as a common edge, wherein the edge is rounded with an edge radius. The transition portion is in this case defined by the rounded connection portion. The edge radius is preferably between 2 and 10 mm. The two surface portions define, for example, an angle β of from 90°≤β≤135° (cf. FIG. 1: β1 and β2).
The at least one recess may further be constructed as a channel-like notch or indentation. In principle, the cross-section of the recess may be formed, for example, in a V-shaped or U-shaped manner. However, other cross-sections are also able to be used as long as a sufficient discharge of matrix from the recess to the semi-finished fiber product can be achieved in the region of the transition portion.
Furthermore, an extent direction of the at least one recess may be orientated at an angle α between 0°<α≤±90°, preferably between ±30°<α≤±60°, in particular of substantially α=±45°, relative to an extent direction of the curved transition portion.
According to another embodiment, the curved transition portion has at least two recesses, wherein the recesses are orientated parallel with each other in the extent direction thereof. A plurality of recesses which each have a spacing of from 2 to 20 mm, particularly preferably from 5 to 10 mm, relative to the adjacent recess may preferably be provided.
Additionally or alternatively, the curved transition portion may have at least two recesses, wherein the two recesses are orientated relative to each other at an angle γ between 0°<γ≤±90°, preferably between ±30°≤γ≤±90°, in particular of substantially γ=±90°. The correspondingly orientated recesses may be arranged with spacing from each other or in an intersecting manner.
The at least one recess preferably has a depth of at least 0.5 mm, preferably at least 2 mm, particularly preferably a depth between 2 mm and 3 mm. The geometry of the recesses is preferably selected in such a manner that a negative influence of the semi-finished fiber product, for example, as a result of introduction of the semi-finished fiber product into the recess, is (substantially) prevented. In this case, a width of the recess or the opening thereof with respect to the cavity of from 1 to 10 mm, preferably from 2 to 5 mm, is advantageous.
In principle, the pressing tool may be constructed as an RTM tool or as a wet pressing tool.
Although the above explanations have always been set out in connection with the best possible matrix flow in the semi-finished fiber product in the context of a resin injection, the explanations apply similarly to wet-pressing of a semi-finished fiber product which has already been pre-impregnated. In this case, there may also be produced a local displacement of the matrix in the semi-finished fiber product, and consequently destruction of the complete impregnation, as a result of high degrees of deformation in particular in the region of powerfully curved transition portions. In this case, the recesses also allow the provision of a compensating resin flow into the transition portion and, consequently, also prevent the production of dry locations or pores.
It will be understood that the tool portion described may have one or more of the transition portions described. They may also have an identical or different number, arrangement and orientation of the recesses.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.